Dual stage vacuum chamber with full circuit board support

ABSTRACT

A dual-stage fixture for a circuit tester includes a slide plate that can be slid between at least a first position and a second position. In the first position, an upper stripper plate is spring-loaded, and a full set of test probes, including both long-stroke and short-stroke probes, can contact the circuit board or UUT (unit under test). In the second position, the upper stripper plate becomes fixed in position, and only the long-stroke probes can contact the circuit board. The fixed positioning of the upper stripper plate prevents the short-stroke probes from contacting the circuit board even when there is unbalanced loading of probe pressure between the top and bottom of the circuit board, thereby preventing transient signals from interfering with testing. In addition, a vacuum is applied in this position during a non-powered test.

TECHNICAL FIELD

This disclosure relates generally to test equipment. More particularly,the disclosure relates to test equipment for circuit boards.

BACKGROUND

Circuit board testers are used for testing a variety of circuit boardsor UUT (unit under test which may be something other than a circuitboard—the terms will be used interchangeably to refer to allpossibilities) or similar devices to assure that the circuit boardsoperate as intended. In at least one type of circuit board tester, suchas Agilent Model No. 3070, Series 3, a separate device, referred to as afixture, is used to position the circuit board such that a plurality ofelectrically conductive probes (which are part of, or coupled to, thetester) contact predetermined components or positions of the circuitboard. The particular components or positions that are contacted by thetest or probes depend on the tests that are desired. When the probes arein contact with the desired locations on the circuit board, electricalsignals with predetermined parameters (e.g., predetermined magnitudes orpatterns of current, voltage frequency, phase, and the like) are appliedby the tester, typically under control of a computer, to certain of theprobes. Some or all of the probes are used to measure the performance orresponse of the circuit board (i.e., to measure electrical parameters atsome or all of the probes contacting the circuit board). In this way, itis possible to rapidly perform a number of tests or measurementscharacterizing the performance of the circuit board while simulating theconditions the circuit board would have, or could have, during actualuse. Although it is possible to use these types of tests and testingdevices for a variety of possible purposes (such as “spot checking”selected circuit boards at a production facility, testing circuit boardswhich may be malfunctioning, testing prototype circuit boards as part ofa design program, and the like), in at least some applications, circuitboard testing is used to provide quality assurance on all orsubstantially all products of a given type or class which are producedby a company.

Some circuit board testers use a vacuum fixture that uses atmosphericpressure, specifically a vacuum, to drive a platen with a combination ofspring-loaded probes and circuit board push down features to pressagainst the circuit board and press it against another platen with afield of spring-loaded test probes. In some circuit board testers, allof the probes contact the circuit board simultaneously. While vacuumsystems are effective, they are quite complex and expensive tomanufacture.

Some circuit board testers use what is known as a dual-stage testfixture. A dual-stage test fixture typically has spring-loaded testprobes that are of two different lengths, known as long-stroke probesand short-stroke probes. As a result, different test cycles can involvedifferent test probes contacting the circuit board. For example, duringa powered in-circuit test, both the long- and short-stroke probescontact the circuit board being tested at the same time. On the otherhand, during a non-powered test, only the long-stroke probes contact thecircuit board. Contacting the circuit board with only the long-strokeprobes allows different circuits on the circuit board to be testedwithout introducing electrical interference by contacting the circuitboard with all of the probes.

In some conventional circuit board testers employing dual-stage testfixtures, however, during the non-powered test, both sides of thecircuit board may not be fully supported. As a result, some of theshort-stroke probes can contact the circuit board during the non-poweredtest, potentially inadequate contact force and poor signal quality andinterference. This interference can cause the test to fail and may causeelectrical damage to the electronic components of the circuit board.Failure to fully support the circuit board at all times may cause thecircuit board to be subject to deformations typically caused by vacuumpressure differentials that can lead to stress fractures in the solderconnections or in the electronic components on the circuit board. Byfully supporting the board/UUT, and eliminating pressure stressesthereon, the quality of test is improved, while simultaneously reducingthe complexity of the tester.

SUMMARY OF THE DISCLOSURE

According to various example embodiments, a dual-stage fixture for acircuit tester includes a slide plate that can be slid between at leasta first position and a second position. In the first position, an upperstripper plate is spring-loaded, and a full set of test probes,including both long-stroke and short-stroke probes, can contact thecircuit board. In the second position, the upper stripper plate becomesfixed in position, and only the long-stroke probes can contact thecircuit board. The fixed positioning of the upper stripper plateprevents the short-stroke probes from contacting the circuit board evenwhen there is unbalanced loading of probe pressure between the top andbottom of the circuit board, thereby preventing transient signals frominterfering with testing. In addition, a vacuum is applied in thisposition during a non-powered test.

One embodiment is directed to a circuit tester for testing a circuitboard. The circuit tester includes a housing having first and secondparts pivotally connected at one edge to be hinged together, or simplythat the parts can be brought closer together not necessarily bypivoting, such as on rails or pins. A push plate is mounted to the firstpart of the housing, and a bottom probe plate is mounted proximate thesecond part of the housing. The bottom probe plate has a first set offirst test probes having a first length and a second set of second testprobes having a second length shorter than the first length. The circuittester also includes a jumper plate that is mounted to the push platevia a plurality of rigid support members. Each rigid support member isconnected to the jumper plate via a respective spring or other biasmember. An upper stripper plate is mounted to the jumper plate via aplurality of resilient members. The stripper plate can also be unitarywith the probe plate so reference to the probe plate can refer to aplate having both functions. A lower plate is mounted to the bottomprobe plate. A first slide plate having apertures formed in it ismovable between a first position and a second position. The first slideplate has a surface that contacts the rigid support members when thefirst slide plate is in the first position. When the first slide plateis in the second position, the rigid support members are received by theapertures. When the first slide plate is in the first position, thefirst test probes and the second test probes contact the circuit board.When the first slide plate is in the second position, only the firsttest probes contact the circuit board.

Another embodiment is directed to a method of using the circuit testerto test a circuit board. The method involves placing the circuit boardin the circuit tester. A vacuum is applied to the circuit tester whenthe first slide plate is in the first position, thereby causing thefirst test probes and the second test probes to contact the circuitboard. An in-circuit test is performed on the circuit board, and thevacuum is released. The first slide plate is then moved from the firstposition to the second position. The vacuum is applied to the circuittester when the first slide plate is in the second position, therebycausing only the first test probes to contact the circuit board. A socalled functional test is then performed on the circuit board.

Also disclosed is a method for testing a circuit board or UUT (unitunder test), the method in a circuit tester having at least some ofthese elements: first and second parts capable of being brought closertogether; a push plate mounted to the first part; a probe plate adjacentthe push plate for first and second test probes; a rigid support memberattached to either plate at one end; a slide plate laterally movablebetween a first position and a second position, the slide plate having asurface that contacts the rigid support members when the slide plate isin the first position, the slide plate or probe plate having anapertures for receiving the rigid support member in the second position.The method involves placing the UUT in the circuit tester. A force isapplied to the circuit tester when the slide plate is in the firstposition, thereby causing the first test probes and the second testprobes to contact the UUT. An in-circuit test is performed on the UUT.At least some force is released. The slide plate is moved from the firstposition to the second position. The force is applied to the circuittester when the slide plate is in the second position, thereby causingonly the first test probes to contact the UUT. A functional test isperformed on the UUT.

The disclosed embodiments may realize certain advantages. For instance,with the vacuum applied during the non-powered test, the spring-loadedlong-stroke test probes can make a more positive electrical contact withthe circuit board. By contrast, in some conventional circuit testersthat use mechanical means to bring the test probes into contact with thecircuit board, the mechanical forces exerted on the circuit board cancause the probe plates bearing the test probes to bow away from thecircuit board, reducing the probe travel and, in turn, limitingsuccessful electrical contact.

Further, in the disclosed embodiments, the upper stripper plate isspring-loaded during the powered test, but becomes fixed in place duringthe non-powered test. As a result, the fixed plate provides a positivedelta between the long- and short-stroke test probes, preventing theshort-stroke probes from contacting the circuit board during thenon-powered test. In addition, the fixed plate provides an even andregulated pressure against the circuit board when it is being tested,preventing strain events that can cause structural damage to the circuitboard and its electronic components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a side plan view in section of a circuit tester in arest configuration according to one embodiment.

FIG. 2 illustrates a side plan view in section of the circuit tester ofFIG. 1 in a first test configuration.

FIG. 3 illustrates a side plan view in section of the circuit tester ofFIG. 1 in a second test configuration.

FIG. 4 illustrates additional components of the side plan view of FIG. 1in a rest configuration.

FIG. 5 illustrates additional components of the side plan view of FIG. 2in first test configuration.

FIG. 6 illustrates additional components of the side plan view of FIG. 3in second test configuration.

FIG. 7 illustrates a top plan view of the circuit tester of FIG. 1.

FIG. 8 illustrates an exploded view of the circuit tester of FIG. 1.

DETAILED DESCRIPTION

The inventive subject matter is described with specificity to meetstatutory requirements. However, the description itself is not intendedto limit the scope of this patent. Rather, it is contemplated that theclaimed subject matter might also be embodied in other ways, to includedifferent steps or combinations of steps similar to the ones describedin this document, in conjunction with other present or futuretechnologies.

Dual stage testing devices are known in the art. To aid the reader inunderstanding the basic technology prior to this disclosure, referenceshould be had to U.S. Pat. No. 8,004,300, the disclosure of which isincorporated by reference and shows a testing environment. FIG. 1 ofthat patent shows a testing device in perspective with a UUT (unit undertest) shown as a circuit board. The UUT is removably and rigidlyattached to, and optionally, spaced apart from, a support plate ormounting plate with or without spacer elements. In this configuration,the electrical contacts on the UUT that are to be tested face upward,and are accessible to various probes from above or below plate 18. Theremay also be probes from underneath the UUT. In this case, probes fromthe top are illustrated. Note that the circuit board and fixture onwhich it is mounted are considered one for the purpose of thisapplication, though they are likely to be separate components. We referto the circuit board whether or not it includes a fixture. The probesmay apply and measure voltages or currents at various locations on theUUT, and are controlled mechanically and electrically by the tester. Acomputer, not shown, may control the tester and may record data from thetests.

According to various disclosed embodiments, a dual-stage fixture usesatmospheric pressure, e.g., a vacuum, as a driving force to press a pushplate down. A jumper plate is mounted on rods, called jumper standoffs,to the push plate. The jumper plate may or may not have spring-loadedprobes. Any such spring-loaded probes can be long-stroke, short-stroke,or a combination of long- and short-stroke probes. The jumper plate ismounted in such a way as to allow it to move loosely in the x- andy-axes. Movement in the z-axis is variable.

Mounted to the jumper plate is a smaller plate, called an upper stripperplate, with clearance holes through which the test probes can protrude.The upper stripper plate is spring-loaded through the use of pushpinassemblies. As a pushpin assembly is depressed, a plunger assemblyprotrudes through a rear assembly by an equal amount to that which it isdepressed. The circuit board lies upon a similarly mounted stripperplate above a platen of long- and short-stroke test probes.

In a first test cycle, when a force, such as from a vacuum or othersource of force such as mechanical, electromagnetic, or pneumatic, allof which will simply be referred to as vacuum, is applied to thedual-stage fixture, the push plate is drawn down, forcing the upperstripper plate to contact the circuit board. As a result, the circuitboard is pressed down against the lower probe field. As the push plateis drawn down, all of the spring-loaded probes make contact with thecircuit board and the circuit board is tested. The vacuum is thenreleased.

In a second test cycle, a plate, called a slide plate, that is mountedto the underside of the push plate is slid from a first position to asecond position. The slide plate has a number of clearance cutouts forjumper plate standoffs that are mounted on the back of the jumper plate.When the slide plate is moved into one position, the jumper plate'sstandoffs can contact the surface of the slide plate. When the slideplate is moved into a different position, on the other hand, thestandoffs align with the clearance cutouts and contact the bottom of thepush plate. This, in effect, varies the mounting height of the jumperplate, thus allowing either all of the probes to contact the circuitboard or just a subset, e.g., only the long-stroke probes.

The upper stripper plate rests upon spring-loaded pushpin assemblies. Asthe pushpin assembly's plunger is depressed, the plunger's shaftprotrudes an equal distance from the opposite side. Mounted on the slideplate are buttons that align with the spring-loaded pushpins when theclearance cutouts align with the jumper plate standoffs. When the slideplate's buttons align with the spring-loaded pushpins, they force thespring-loaded pushpins to lock in place, thereby losing their springcharacteristics. Accordingly, in this configuration, the upper stripperplate is fixed in position and prevents the short-stroke probes fromcontacting the circuit board. Even though the short-stroke probes do notcontact the circuit board in this configuration, the circuit board isstill pressed against the long-stroke probes of either the upper probefield or the lower probe field by a solid surface. A non-poweredfunctional test is performed. When the functional test is completed, thevacuum is released, and all of the probes are disengaged.

FIGS. 1 and 4 illustrate an example circuit tester 100 into which acircuit board 102 can be placed for testing. FIG. 7 shows a top planview of the circuit tester 100. FIG. 8 shows an exploded view of thecircuit tester 100. FIGS. 1 and 4 illustrate the circuit tester 100 in arest position. The circuit tester includes a housing having a firstportion and a second portion that are connected at one edge by anoverclamp 104, which serves as a hinge to facilitate access to thecircuit board 102. A push plate 106 is mounted to the first portion ofthe housing. A bottom probe plate 108 is mounted proximate the secondportion of the housing. The bottom probe plate 108 has a lower probefield including a number of long-stroke probes 110 and a number ofshort-stroke probes 112 that are shorter than the long-stroke probes110.

A jumper plate 114 is mounted to the push plate 106 by a number of rigidsupport members 116, called jumper plate standoffs. An upper stripperplate 120, which can also perform as a probe plate or adjacent to aprobe plate, is mounted to the jumper plate 114 by resilient members122, which include springs 118. In the embodiment shown in FIG. 4, theupper stripper plate 120 has clearance holes through which an upperprobe field can protrude. The upper probe field includes a number oflong-stroke probes 124 and a number of short-stroke probes 126 that areshorter than the long-stroke probes 124. These test probes may be ofsimilar or different lengths to the test probes of the lower probefield.

A seal plate (also referred to as a stripper plate) 128 is mounted tothe bottom probe plate 108. It is also possible that they built as thesame plate so the words can be used interchangeably. The seal plate 128may have clearance holes through which the lower probe field canprotrude. The seal plate 128 and the upper stripper plate 120 may haveadditional clearance holes through which support members for supportingthe circuit board can protrude.

The circuit tester 100 also includes one or more slide plates that aremovable to control which test probes can contact the circuit board. Anupper slide plate 130 is movable between at least first and secondpositions, as described more fully below. When the upper slide plate 130is in the first position, a surface of the upper slide plate 130contacts the rigid support members 116. The upper stripper plate 120 isspring-loaded, and both the long-stroke probes 124 and the short-strokeprobes 126 can contact the circuit board 102. On the other hand, whenthe upper slide plate 130 is in the second position, apertures 132, 134formed in the upper slide plate 130 receive the rigid support members116. Generally members 116 and apertures 123/134 will be coaxiallyaligned when they pass through, but such coaxial alignment is intendedto mean that support passes through the aperture even if the axis is notin the center of the aperture which may occur, for example, in oversizedapertures, oblong apertures, or similar apertures. In the preferredembodiment, the apertures are just large enough to receive thesupport(s). As a result, the upper stripper plate becomes fixed inposition, and only the long-stroke probes 124 can contact the circuitboard 102. The fixed positioning of the upper stripper plate 120prevents the short-stroke probes 126 from contacting the circuit board102 even when there is unbalanced loading of probe pressure between thetop and bottom of the circuit board, thereby preventing transientsignals from interfering with testing. Notice that the rigid supportmember(s) can also be attached to at the opposite end (i.e., the slideplate and then the apertures 132 and 134 would be on the jumper and/orstripper plates resulting in the same function in the same way with thesame result). Reference to the structure as shown in the figurescontemplates both arrangements.

In the embodiment shown in FIG. 1, a lower slide plate 136 located underthe seal plate 128 is also movable between first and second positions.The lower slide plate 136 has rigid support members 138, 140 attached toit. When the lower slide plate 136 is in the first position, the rigidsupport members 138, 140 are received by corresponding apertures 142,144 formed in the seal plate 128, allowing both the long-stroke testprobes 110 and the short-stroke test probes 112 of the lower probe fieldto contact the circuit board. On the other hand, when the lower slideplate 136 is in the second position, the rigid support members 138, 140contact a lower surface of the seal plate 128, preventing theshort-stroke test probes 112 from making contact with the circuit board.The upper and lower slide plate systems may be constructed essentiallythe same (though thicknesses shown are different to accommodate spaceavailability). The preferred embodiment contemplates both upper andlower slide plate systems so that two-stage testing can be conductedwith probes on the bottom and top. They may operate in unison orseparately so that different tests can be conducted on the bottom or toptest points on the circuit board in at least four different test modes:top only, bottom only, top simultaneously with bottom or sequentially.

In operation, FIG. 1 shows the circuit tester 100 in a rest position,that is, when no testing is being performed. In this position, no vacuum(or vacuum alternatives) is applied to the circuit tester 100. As aresult, a resilient material 146, such as foam or a bellows, isuncompressed. The amount of travel provided by the vacuum can be variedby using materials with different degrees of resiliency, such as more orless rigid foam or a bellows mechanism. With no vacuum applied, the pushplate 106 is not urged toward the circuit board 102. The jumper plate114 does not contact the surface of the rigid support members 116. Theupper stripper plate 120 can also be compressed by hand. The circuitboard is supported by support pins 148, 150, but preferably no testprobes contact the circuit board in rest mode.

FIGS. 2 and 5 show the circuit tester 100 in a configuration to performa powered in-circuit test. In this so-called in-circuit testconfiguration, the upper slide plate 130 is in the first position. Asshown in FIG. 2, the rigid support members 116 contact a lower surfaceof the upper slide plate 130. When the vacuum is applied, the resilientmaterial 146 compresses to form a seal, and the push plate 106 is urgedtoward the circuit board 102. The jumper plate 114 is effectively set ata low mounting height (maximum travel), allowing both the long-strokeprobes 124 and the short-stroke probes 126 of the upper probe field tocontact the circuit board 102. The jumper plate 114 does not contact thesurface of the rigid support members 116. The lower slide plate 136 isalso in the first position. In this position, the rigid support members138, 140 are received by corresponding apertures or recesses 142, 144formed in the seal plate 128, allowing both the long-stroke test probes110 and the short-stroke test probes 112 of the lower probe field tocontact the circuit board. After the in-circuit test is performed, thevacuum is released.

FIGS. 3 and 6 show the circuit tester 100 in a different configurationto perform an unpowered functional test. In this functional testconfiguration, the upper slide plate 130 is in the second position andthe vacuum is again applied. As shown in FIG. 3, the rigid supportmembers 116 are received in the apertures or recesses 132, 134 of theupper slide plate 130. The resilient members/springs 122 come intocontact with rigid support members 152, 154 that are secured to theupper slide plate 130. The rigid support member 152, 154 act as deadstops that limit the motion of the resilient members 122 and, as aresult, the jumper plate 114 and the upper stripper plate 120. Further,the jumper plate 114 contacts the surface of the rigid support members116. With the motion of the jumper plate 114 and the upper stripperplate so limited, only the short-stroke test probes 112 of the upperprobe field can contact the circuit board 102. The lower slide plate 136is also in the second position. In this position, the rigid supportmembers 138, 140 encounter the surface of the seal plate 128, preventingthe short-stroke test probes 112 of the lower probe field fromcontacting the circuit board. Only the long-stroke test probes 110 cancontact the circuit board during the functional test. After thefunctional test is performed, the vacuum is released.

The upper slide plate 130 and the lower slide plate 136 can be movedbetween the first and second positions using any of a variety ofmechanisms, including but not limited to, pneumatic, magnet,electromagnetic, manual and gravity. For example, the slide plates canbe pneumatically driven using a pneumatic air system including an aircylinder 160, as shown in FIG. 7. Alternatively, the slide plates can bemoved using a solenoid. As still another alternative, the slide platescan be moved between the first and second positions manually.

It will be appreciated that, while FIGS. 2 and 3 depict the upper slideplate 130 and the lower slide plate 136 as being movable in unison, insome embodiments, the upper slide plate 130 and the lower slide plate136 are movable independently of one another. That is, in someembodiments, it is possible for the upper slide plate 130 to be in thefirst position while the lower slide plate 136 is in the secondposition, or vice versa. This may allow additional testing protocols tobe realized.

In still other embodiments, the upper slide plate 130 and/or the lowerslide plate 136 may be movable between more than two positions. In suchembodiments, additional levels of testing may be implemented. Forexample, more than two different probe lengths could be used, withdifferent subsets of test probes contacting the circuit board duringdifferent testing protocols.

As demonstrated by the foregoing discussion, various embodiments mayprovide certain advantages. For instance, with the vacuum applied duringthe non-powered test, the spring-loaded long-stroke test probes can makea more positive electrical contact with the circuit board.

It will be understood by those who practice the embodiments describedherein and those skilled in the art that various modifications andimprovements may be made without departing from the spirit and scope ofthe disclosed embodiments. The scope of protection afforded is to bedetermined solely by the claims and by the breadth of interpretationallowed by law.

1.-17. (canceled)
 18. A circuit tester for testing a circuit board orUUT (unit under test), the circuit tester comprising: a housing havingfirst and second parts capable of moving toward and away from each othera push plate mounted; a bottom probe plate mounted proximate the secondpart of the housing and having a first set of first test probes having afirst length and a second set of second test probes having a secondlength than the first length; a jumper plate; at least one rigid supportmembers mounting the jumper plate to the push plate, the at least onerigid support member connected to the jumper plate via a respective biasmember; a plurality of resilient members; and a first slide plateselectively movable between a first by-pass position and a secondblocking position to determine which probes will reach the UUT, thefirst slide plate having a surface that contacts the rigid supportmembers when the first slide plate is in the first position, the firstslide plate having at least one aperture formed and sized to receive asupport member when generally aligned to pass therewith therein forreceiving the rigid support members when the first slide plate is in thesecond position to allow the support member to pass therethrough;wherein, when the first slide plate is in the first position, the firsttest probes and the second test probes contact the UUT and, when thefirst slide plate is in the second position, only the first test probescontact the UUT when the support member are misaligned and cannot passthrough the aperture so that they cannot contact the UUT.
 19. Thecircuit tester of claim 18, wherein an upper stripper plate is mountedto the jumper plate via a plurality of resilient members; the jumperplate has a third set of third test probes having a third length and afourth set of fourth test probes having a fourth length shorter than thefourth length, and wherein the upper stripper plate has a plurality ofapertures formed therein for receiving the third test probes and thefourth test probes.
 20. The circuit tester of claim 19, wherein thethird length is substantially similar to the first length and the fourthlength is substantially similar to the second length.
 21. The circuittester of claim 18, wherein the first slide plate is pneumaticallydriven.
 22. The circuit tester of claim 18, further comprising asolenoid arranged to move the first slide plate between the firstposition and the second position.
 23. The circuit tester of claim 18,wherein the first slide plate is manually movable between the firstposition and the second position.
 24. The circuit tester of claim 18,further comprising a seal plate mounted to the bottom probe plate; asecond slide plate located under the seal plate and movable between afirst position and a second position, the second slide plate having aplurality of rigid members secured thereto, the seal plate having aplurality of apertures formed therein for receiving the rigid members ofthe second slide plate when the second slide plate is in the firstposition.
 25. The circuit tester of claim 18, wherein the first testprobes and the second test probes are spring-loaded.
 26. A method fortesting a circuit board or UUT (unit under test), for use in a circuittester having a housing; a first set of first test probes having a firstlength and a second set of second test probes having a second lengthshorter than the first length; a plurality of rigid supports; and afirst slide plate movable between a first position and a secondposition, the first slide plate having a surface that contacts the rigidsupport members when the first slide plate is in the first position, thefirst slide plate having a plurality of apertures formed therein forreceiving the rigid support members when the first slide plate is in thesecond position; the method comprising: placing the UUT in the circuittester; applying a force to the circuit tester when the first slideplate is in the first position, thereby causing the first test probesand the second test probes to contact the UUT; performing an in-circuittest on the UUT; releasing the force; moving the first slide plate fromthe first position to the second position; applying the force to thecircuit tester when the first slide plate is in the second position,thereby causing only the first test probes to contact the UUT; andperforming a functional test on the UUT.
 27. The method of claim 26 ontester having a third set of third test probes having a third length anda fourth set of fourth test probes having a fourth length shorter thanthe fourth length, and a plurality of apertures formed in a plate forreceiving the third test probes and the fourth test probes.
 28. Themethod of claim 27, wherein the third length is substantially similar tothe first length and the fourth length is substantially similar to thesecond length.
 29. The method of claim 26, further comprising actuatinga pneumatic mechanism to move the first slide plate between the firstposition and the second position.
 30. The method of claim 26, furthercomprising activating a solenoid to move the first slide plate betweenthe first position and the second position.
 31. The method of claim 26,further comprising manually moving the first slide plate is between thefirst position and the second position.
 32. The method of claim 26,wherein the circuit tester further comprises a second slide platelocated under the seal plate and movable between a first position and asecond position, the second slide plate having a plurality of rigidmembers secured thereto, the seal plate having a plurality of aperturesformed therein for receiving the rigid members of the second slide platewhen the second slide plate is in the first position.
 33. The method ofclaim 26, wherein the first test probes and the second test probes arespring-loaded.
 34. A method for testing a circuit board or UUT (unitunder test), the method in a circuit tester having first and secondparts capable of being brought closer together; a support memberattached to either plate at one end; and a slide plate laterally movablebetween a first position and a second position, the slide plate having asurface that contacts the support members when the slide plate is in thefirst position, the slide plate or probe plate having an apertures forreceiving the support member in the second position; the methodcomprising the steps of placing the UUT in the circuit tester; applyinga force to the circuit tester when the slide plate is in the firstposition, thereby causing the first test probes and the second testprobes to contact the UUT; performing an in-circuit test on the UUT;releasing at least some force; moving the slide plate from the firstposition to the second position; applying the force to the circuittester when the slide plate is in the second position, thereby causingonly the first test probes to contact the UUT; and performing afunctional test on the UUT.